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Viscera:Prostate
The prostate gland is part of the male reproductive system and is the largest male accessory gland and provides approximately 30% of the volume of seminal fluid. It typically weighs between 20-40 grams with an average size of 3 x 4 x 2cm. The prostate is comprised of 70% glandular tissue and 30% fibromuscular or stromal tissue. The prostate gland is an inverted pyramid that surrounds the prostatic urethra, which traverses the prostate close to its anterior surface. The seminal vesicles are superior and posterior to the prostate gland. Its ejaculatory ducts pierce the posterior surface of the prostate below the bladder * Base: fused with the neck of the bladder * Apex: lowest part, contact with the urogenital diaphragm * Anterior surface: forms the back of the retropubic space and connected to the pubic bone by the puboprostatic ligaments . * Inferolateral surface: rests on the levator ani fascia * Posterior surface: triangular and flat, lie anterior to the rectum and has a vertical median groove. It is separated from the rectum by the rectovesical fascia. This is palpable via a rectal exam. The ejaculatory ducts enters here. Prostate is histologically composed of glandular (acinar) and nonglandular elements * Two nonglandular elements: Prostatic urethra and AFMS ** AFMS is contiguous with bladder muscle and external sphincter *** ~ 30% of prostate volume ** Proximal half of prostatic urethra is surrounded by cuff of smooth muscle ("preprostatic sphincter") * Glandular prostate consists of outer and inner components * Inner prostate has two parts: Periurethral glandular tissue and transitional zone ** Periurethral glands *** < 1% of normal glandular prostate *** Small glands confined to submucosal layer of proximal prostatic urethra above verumontanum and deep to preprostatic sphincter *** Ducts drain into proximal posterolateral wall of prostatic urethra in two rows ** Transitional zone *** ~ 5% of normal glandular prostate *** Surrounds anterior and lateral aspects of proximal urethra *** Involvement in BPH causes bladder outlet obstruction because of urethral compression * Outer prostate has two parts: Central and peripheral zones ** Central zone *** ~ 25% of normal glandular prostate *** Surrounds ejaculatory ducts *** Funnel-shaped with its widest portion making majority of prostatic base *** Tapered tip extends inferiorly to level of verumontanum *** Encloses both periurethral glands and TZ *** Ducts of CZ drain to region of verumontanum, clustered around entry of ejaculatory ducts ** Peripheral zone *** ~ 70% of the normal glandular prostate *** Surrounds both CZ and distal prostatic urethra *** Ducts of PZ drain exclusively to distal prostatic urethra The prostate gland has a true capsule which is a thin layer of connective tissue at the periphery of the prostate gland, and a fibrous pseudocapsule formed by 3 distinct layers of fascia; the anterior, lateral, and posterior fasciae. The prostatic venous plexus lies between the true capsule and pseudocapsule. Neurovascular bundles travel posterolaterally at 5 and 7 o'clock and give off branches into the prostate at the apex and base. The prostatic urethra 3-4cm in length, pass through the prostate. A midline ridge called urethral crest, projects into the lumen from the posterior wall. Shallow depression on either side is called prostatic sinus. Midlline rounded eminence called verumontanum open into the crest. Proximal part of the prostatic urethra (preprostatic), is surrounded by smooth muscles which extends from the muscles of the bladder neck. Relations * anteriorly: pubic symphysis * inferiorly: urogenital membrane * superiorly: bladder * posteriorly: rectum * laterally: prostatic venous plexus and levator ani Blood supply * arterial supply: prostatic branch of inferior vesical artery (a division of the internal iliac artery); sometimes supplied by the middle rectal arteries * venous drainage: prostatic venous plexus in communication with the pudendal plexus to the deep dorsal vein (to the internal iliac vein). ** this communicate with the vertebral venous plexus (a route of cancer spread) Nerve supply * parasympathetic pelvic splanchnic nerves via inferior hypogastric plexus(S2-S4) and sympathetic (L1-L2) from the inferior hypogastric plexus. Lymphatic supply * drainage mainly to obturator and internal iliac nodes * some drainage to external iliac, presacral and para-aortic nodes Normal variant * congenital cyst * additional lobes * variable prostate size * variable ejaculatory duct course, e.g. caudal formation of ducts